Gelatin has a wide range of commercial utility. For example, gelatin is used in wet processed photographic emulsions, pharmaceutical dosage forms, cosmetics (binder), and a wide range of food products. Gelatin has many useful physical and chemical properties that support this broad range of utility.
Gelatin is manufactured by the hydrolysis of animal by-products that contain collagen. This is usually found in animal bones, skins, and connective tissue. The collagen containing material is heated in water and the liquor produced is concentrated and dried, leaving behind the colorless or pale yellow protein that constitutes the hydrophilic colloid material known as gelatin.
The primary sources of gelatin are from bovine and swine animals. Additionally, fish and poultry are alternative small volume sources of gelatin. The source of gelatin can be a problem for potential areas of use or for particular consumers. Large groups around the world choose not to ingest any products of pigs (e.g., vegetarians, Hebrews, and Muslims) or the products of beef (e.g., vegetarians and Hindus). As medication and/or diet supplements are provided in gelatin capsules without any indication of the source of the gelatin, the use of capsules is restricted in areas where religious beliefs question the source of the gelatin. Additionally, due to reported possibilities of cross-contamination of diseases among species, for example bovine spongiform encephalopathy (“BSE” or “Mad Cow Disease”), the use of uncontrolled by-products from animals has lost some level of commercial acceptance. In short, there is a need for replacement compositions for gelatin that are not derived from animal sources.
Carrageenan is a natural hydrocolloid, more particularly a polysaccharide hydrocolloid, which is derived from red seaweed, particularly of the species Rhodophycea. Carrageenan is a carbohydrate polymer of repeating galactose and 3,6-anhydrogalactose (sugar) units that is linear and without significant numbers of branches or substitutions. Most, if not all, of the galactose units on a carrageenan molecule possess a sulfated ester group. The exact position of the sulfate groups, the cations on the sulfate groups, and the possible presence of an anhydrous bridge on the molecule differentiate the various types of carrageenan.
There are five distinct types of carrageenan, each of which behaves differently and has distinct properties. The types of carrageenan are iota, kappa, lambda, mu and nu carrageenan. These types of carrageenan can significantly vary in properties. For example, lambda carrageenan in solution is unable to associate into a structure, and therefore is unable to form a gel, but nonetheless acts as a thickener. Both kappa and iota carrageenan, the predominant carrageenan types, are able to form gels. Kappa carrageenan is known to form strong gels in the presence of potassium cations. However, kappa carrageenan gels tend to be brittle and exhibit syneresis (exudation of the liquid portion of the gel). Iota carrageenan tends to react strongly to calcium cations and forms a weaker and more flexible gel than kappa carrageenan. Iota carrageenan is not as susceptible to syneresis as kappa carrageenan. Mu and nu carrageenan are thought to be precursors of kappa carrageenan and iota carrageenan, respectively, and may be present only in very small quantities as impurities in pure kappa and iota carrageenan. Mu and nu carrageenan are not of commercial importance.
The type of carrageenan used affects the physical properties of the final gel or film. WO 99/07347 and WO 01/03677 describe gel forming compositions that have iota carrageenan as the sole gelling agent. Despite the fact that kappa carrageenan is also able to gel, these publications teach that kappa carrageenan is detrimental when the end product desired is a film for capsule manufacture. The phenomenon of syneresis and the fact that kappa carrageenan forms brittle gels are cited as reasons for avoiding the use of kappa carrageenan in such films.
When forming a film for subsequent use in medicinal, cosmetic, or nutritional capsule manufacture, the resultant physical properties of sealability, extensibility, and tensile strength are important. Thus, a gelling composition comprising carrageenan must provide adequate physical properties useful in manufacturing. Kappa carrageenan is a less expensive starting material as compared to iota carrageenan. Thus, it would be beneficial to develop a gel- or film-forming composition comprising kappa carrageenan and iota carrageenan, wherein the resultant film provides the requisite physical properties for capsule manufacture.